# Exploring allomelanin: A comparative analysis via natural product extraction and synthesis

## TL;DR

This study compares natural and synthetic allomelanin, finding that copolymerization better mimics natural structures and properties.

## Contribution

The study reveals that copolymerization of 1,8-DHN with catechol or tannic acid better replicates natural allomelanin.

## Key findings

- Simple homopolymerization of 1,8-DHN does not match natural allomelanin structures.
- Copolymerization with catechol or tannic acid yields materials with properties similar to natural allomelanin.
- Natural allomelanins show high porosity, up to 155 square meters per gram.

## Abstract

Allomelanin is a nitrogen-free class of melanin commonly found in plants and fungi. Although synthetic analogs have been developed from 1,8-dihydroxynaphthalene (1,8-DHN), detailed physicochemical comparisons with natural allomelanins remain limited. Herein, we extracted allomelanin from black knot fungus, chaga mushroom, and black oat using an acid-base extraction protocol, comparing them against a library of synthetic analogs derived from a range of putative, natural precursors. Spectroscopic analyses indicate that simple homopolymerization of 1,8-DHN does not adequately represent natural allomelanin structures. Instead, heterogeneous copolymerization of 1,8-DHN with catechol or tannic acid yields materials with physicochemical properties more consistent with natural extracts. This is also supported by their enhanced antioxidant and dye/metal adsorption properties. Like their synthetic counterparts, extracted natural allomelanins exhibit intrinsic porosity, reaching a Brunauer-Emmet-Teller area of 155 square meters per gram, potentially facilitating nutrient transport and toxin adsorption, although further studies will be required to probe this.

Comparing natural and synthetic allomelanin uncovers copolymerization as key to melanin structure and bioinspired material design.